In the recent large increase in the amount of telecommunications, power consumption tends to increase in any electronic equipment, and lower power consumption is becoming a social concern. In particular, many of the power supply parts of such electronic equipment are mainly made of switching power supplies. Enhancing the efficiency, and reducing the size and noise of this power supply part are technical problems to be addressed. Development of this power supply at high speeds is an important breakthrough in the development of electronic equipment.
Conventionally, this kind of switching power supply has been structured as shown in FIGS. 8 and 9.
Hereinafter, a description is provided of a conventional example with reference to FIGS. 8 and 9. FIG. 8 is a circuit block diagram of a conventional switching power supply. FIG. 9 is a perspective view showing an appearance of the conventional switching power supply.
As shown in FIGS. 8 and 9, generally, a conventional switching power supply is structured so that input circuit part 1, converter part 2, and output circuit part 3 are mounted on single main substrate 9.
Input circuit part 1 is made of input filter 1a, input rectifier circuit 1b, power-factor improvement circuit 4, smoothing circuit 1c and other components. Converter part 2 is made of control circuit 5, transformer 6, primary power element 7, secondary power element 8 and other components. Now, in many cases, a field-effect transistor (hereinafter referred to as a FET) is used as primary power element 7, and a diode is used as secondary power element 8. However, as a switch instead of a diode, a FET is used in some cases. Further, output circuit part 3 is made of output smoothing section 3a, output conversion circuit 3b, output filters 3c and other components.
According to some of the technical references of the prior art of this application, a circuit block including a control circuit is modularized, as disclosed in Japanese Patent Unexamined Publication No. 2001-359281 (Reference 1), No. H5-198445 (Reference 2), and No. 2001-103756 (Reference 3), for example.
According to another technical reference of the prior art of this application, a wiring pattern for transferring the heat of a heat sink attached to a printed coil transformer, primary power element, and secondary rectifier circuit is provided on a mounting substrate, as disclosed in Japanese Patent Unexamined Publication No. H8-45748 (Reference 4).
However, in the constitution of FIGS. 8 and 9, which shows the most common conventional example, each circuit block and all the components are mounted on single main substrate 9. For this reason, the specification of each component delicately relates to and interferes with each other, and thus the determination of final specifications is difficult. This poses the following problems in the efficiency of development and design: a highly experienced person familiar with designing and an extremely long development lead time are necessary. Additionally, when the output of the power supply is increased, the size of transformer 6 mounted on converter part 2 must be extremely increased. The size exceeds the limitation on the shape of the power supply, and the temperature of the transformer rises and exceeds a specified value. Thus, the conventional example also has problems in reduction in the size and heat generation.
In each of the inventions of References 1 through 3, a specific portion is modularized to reduce the size. However, because the portion is a complicated module block that has many components and many functions, including a control circuit, determination of the specifications is much more difficult than that of the conventional example of FIGS. 8 and 9. This significantly increases the time and cost for development, and provides an expensive power supply block. For this reason, these inventions have many problems, e.g. limited fields and applications in market deployment.
In the invention of Reference 4, because the terminals of the transformer and the heat sink are connected by wiring patterns, the pattern design is limited. Additionally, long wirings increase the impedance, noise, and loss in the wirings. Further, because heat is transferred via the wiring patterns and the distance to the heat sink is long, improvement of the heat transfer effect is limited to a certain level. Thus, this invention has many problems.